The present invention relates to an idling revolution contol device for an internal combustion engine in which an idling revolution is controlled to a desired value by controlling an actuator which regulates a degree of opening of a throttle valve.
Such idling revolution control device in which the degree of opening of a throttle valve provided in a suction pipe of an internal combustion engine is regulated to regulate an idling revolution to a desired value functions, generally, to compare an actual revolution number of the engine with a predetermined desired revolution number and feedback-control the actual revolution number to the desired revolution number. However, at a low revolution number in such as idling condition, a time lag from a change of throttle opening to a resultant change of revolution number is large and it is very difficult to obtain a high response of revolution number when a load of the engine is abruptly changed as in a case of operation of an air-conditioner associated therewith. Therefore, it has been usual to use a detector for detecting an actual opening degree of the throttle valve and feedback-control the actual opening degree to maintain it at the desired degree.
In an engine-braking condition during a vehicle mounting the engine runs, i.e., when an accelerator is released while a transmission gear is kept meshed, the engine is driven by the vehicle itself. Therefore, the situation is much different from the idling condition although the throttle valve is in the idle position. On the other hand, in a control device having a fast idle function, a warming-up of the engine proceeds even during the vehicle runs. Therefore, an actuator for controlling an amount of intake air has to be controlled to the closing side with an increase of water temperature. In order to realize this control, a position information of the actuator is used. However, due to a variation of actuator position vs. amount of idle intake air characteristics and/or a variation of idle load engine by engine, there may be a case where the amount of air necessary under idling condition can not be obtained during the deceleration period, causing an operator to feel a lack of deceleration or the engine to stop. This is more severe when the engine is new and the friction loss is considerable.
Further, it has been very difficult to maintain a desired idle revolution when the electric load on the engine due to head lamps, braking lamps and radiator fan motor, etc. which are not considered in the idle revolution control, is changed temporarily.